The invention relates to a seat adjuster having a fixed part, a drive element, an output element, a clamping body coupling arrangement by means of which a back and forth movement of the drive element out of a neutral position and back into the neutral position is converted into a continued movement of the output element in a uniform direction of rotation, and a releasable locking device for locking the output element in a form-fitting manner on the fixed part.
A seat adjuster of this type is known from EP 0 979 179 B2.
Such seat adjusters are used in particular in automotive vehicles for transmitting an adjustment moment from an actuating member onto a gear which drives the part of the vehicle seat to be adjusted, for example for the purpose of seat height adjustment.
When a torque is exerted onto the drive element by means of the actuation member, the clamping bodies are released from their clamping position, so that the drive torque can be transmitted onto the output element. As soon as the drive element is force-free again, the clamping bodies are elastically urged back into the clamping position, so that the drive element is arrested at the fixed part in the position that has then been reached. A one-way clutch assures that, when the drive element returns into the neutral position, only the drive element will be moved, whereas the output element remains in the adjusted position.
A similar seat adjuster is also known from DE 20 2010 007 993 U1, EP 0 743 221 B1 and WO 2012/013234 A1 which describe seat adjusters in which a second clamping body coupling is provided in place of the one-way clutch.
The clamping force generated by the clamping bodies allows the adjustable part of the vehicle seat to be held safely in the adjusted position even when the vehicle seat is subject to very high external forces, e.g. in a collision of the vehicle. However, if the drive element is permanently subject to a torque, e.g. due to the force of weight of a person sitting on the vehicle seat or, if the seat is not occupied, due to a force of a spring that is provided for partly compensating the weight force of the person, a gradual roll-off of the clamping bodies along the clamping contours may occur as a result of vibrations, which results in a gradual undesired adjustment of the seat. For this reason, the document EP 0 979 179 B2 mentioned in the opening part of the description describes a locking device which can achieve an additional form-fitting lock of the drive element in the adjusted position, so that a gradual roll-off of the clamping bodies is prevented. As soon as the actuating member is operated, however, in order to intentionally adjust the vehicle seat, the additional locking action is released automatically. In the known seat adjuster, the locking device is formed by a latch that is arranged outside of the periphery of the clamping body coupling.